Field of the Invention
The present invention relates to a solid-state imaging device and a method of driving the solid-state imaging device.
Description of the Related Art
In recent years, the general use of imaging systems (digital video cameras and digital still cameras and the like) that use CMOS image sensors that are suitable for low-power-consumption requirements and high-speed readout operations has become widespread.
As one example of a CMOS image sensor, Japanese Patent Application Laid-Open No. 2006-262387 discloses a solid-state imaging device configured to generate charges by photoelectric converting incident light by a photoelectric conversion element, transfer the generated charges to a floating diffusion capacitor, and output a pixel signal based on the charges held in the floating diffusion capacitor. The solid-state imaging device disclosed in Japanese Patent Application Laid-Open No. 2006-262387 further includes a charge holding portion connected to the floating diffusion capacitor.
According to the solid-state imaging device disclosed in Japanese Patent Application Laid-Open No. 2006-262387, signal charges that overflow from the photoelectric conversion element during an exposure period can be accumulated in the charge holding portion provided separately from the floating diffusion capacitor. By also reading out the signal charges that overflowed and accumulated in the charge holding portion, the dynamic range of an output signal can be expanded in comparison to the case of reading out only signal charges transferred from the photoelectric conversion element to the floating diffusion capacitor.
Further, after the exposure period of the photoelectric conversion element, correlated double sampling can be performed by reading out an output signal based on a noise charge after resetting the floating diffusion capacitor, and thereafter reading out an output signal based on signal charges accumulated in the photoelectric conversion element after transferring the signal charges from the photoelectric conversion element to the floating diffusion capacitor. Correlated double sampling can also be performed by reading out an output signal based on signal charges overflowed from the photoelectric conversion element after transferring the signal charges from the charge holding portion to the floating diffusion capacitor, and thereafter reading out an output signal based on a noise charge after resetting the charge holding portion. It is thereby possible to perform highly accurate reading out of signals in a manner in which a noise component has been decreased.
However, according to the solid-state imaging device disclosed in Japanese Patent Application Laid-Open No. 2006-262387, when resetting of the floating diffusion capacitor is performed after a charge accumulation period, some of the signal charges that accumulated in the floating diffusion capacitor when the signal charges overflowed are reset in some cases, and therefore the accuracy with respect to reading out the photoelectric conversion signals declines.